Abstract A22: Development and characterization of an oral cancer cell line resist to the cytotoxic effects of the green tea catechin, (-)-Epigallocatechin-3-gallate

Abstract

Abstract (-)-Epigallocatechin-3-gallate (EGCG) is the most abundant polyphenol in green tea (Camellia sinensis). Although many studies have demonstrated its cancer chemopreventive and chemotherapeutic effects, the potential for development of EGCG resistance in cancer cells has not been well-studied. The purpose of this study was to develop and characterize an EGCG-resistant oral squamous carcinoma cell line to understand potential mechanisms of resistance to the cytotoxic effects of EGCG. Exposure of oral squamous carcinoma (SCC-25) cells to gradually increasing concentrations of EGCG (10 – 75 μM) resulted in emergence of an EGCG-resistant phenotype (SCC-25E75R). SCC-25E75R cells were significantly resistant to EGCG-induced growth inhibition compared to SCC-25 cells (IC50=157 μM vs 70 μM). Treatment of SCC-25E75R cells with 75 μM EGCG caused a 34% increase in apoptosis compared to a 200% increase in SCC-25 parental cells treated with the same concentration. Microarray analysis showed that under untreated conditions, 73 genes were differentially expressed (≥4 fold change, p<0.05) between SCC-25 and SCC-25E75R cells. The resistant cells have lower expression levels of tumor suppressor genes including absent in melanoma 2 (AIM) and inhibitor of DNA binding 4 (ID4) suggesting the resistance to tumor inhibition. EGCG treatment (75 μM) induced significant changes (≥1.75 fold change, p<0.05) in 52 genes in SCC-25 and 164 genes in SCC-25E75R cells. Among these, 42 genes were found to be differentially regulated by EGCG between the two cell lines. For example, EGCG induced the DNA-damage-inducible transcript 3 (DDIT3) and heat shock 70kDa protein 5 (HSPA5) in resistant cells more significantly than in sensitive cells. This may result in a greater anti-apoptotic protein in SCC-25E75R cells and thereby confirm resistance to the effects of EGCG. In conclusion, this work represents a preliminary investigation into potential mechanisms of resistance to EGCG, and may be useful in understanding responsiveness of oral cancer, as well as other cancer types, to the treatment effects of EGCG. Citation Format: Ling Tao, Jennifer W. Chen, Jong-Yung Park, Sudathip Sae-tan, Joshua D. Lambert. Development and characterization of an oral cancer cell line resist to the cytotoxic effects of the green tea catechin, (-)-Epigallocatechin-3-gallate. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr A22.